No abstract

Assessment of seismic resilience of critical infrastructure such as liquefied natural gas (LNG) storage tanks, is essential to ensure availability and security of services during and after occurrence of large earthquakes. In many projects, it is preferred to build energy storage facilities in coastal areas for the ease of sea transportation, where weak soils such as soft clay and loose sand with liquefaction potential may be present. In this study, three-dimensional finite element model is implemented to examine the seismic response of a 160,000 m3 full containment LNG tank supported by 289 reinforced concrete piles constructed on liquefiable soil overlaying the soft clay deposit. The seismic soil-structure interaction analysis was conducted through direct method in the time domain subjected to the 1999 Chi-Chi and the 1968 Hachinohe earthquakes, scaled to Safe Shutdown Earthquake hazard level for design of LNG tanks. The analyses considered different thicknesses of the liquified soil deposit varying from zero (no liquefaction) to 15 m measured from the ground surface. The key design parameters inspected for the LNG tank include the acceleration profile for both inner and outer tanks, the axial, hoop and shear forces as well as the von Mises stresses in the inner tank wall containing the LNG, in addition to the pile response in terms of lateral displacements, shear forces and bending moments. The results show that the seismic forces generated in the superstructure decreased with increasing the liquefied soil depth. In particular, the von Mises stresses in the inner steel tank exceeded the yield stress for non-liquefied soil deposit, and the elastic–plastic buckling was initiated in the upper section of the tank where plastic deformations were detected as a result of excessive von Mises stresses. However, when soil liquefaction occurred, although von Mises stresses in the inner tank shell remained below the yield limit, localised stress concentrations were observed in the lower section of the tank near the base, increasing the risk of the elephant foot buckling. The lateral displacements, shear forces and bending moments in the piles increased with increasing depth of the liquefied soil. Indeed, increasing the pile lateral displacement amplified the bending moment at the pile head, thus resulting in increases in the pile bending moments especially when the liquefied soil depth exceeded one third of the entire soil deposit. In particular, the bending moment at the pile head exceeded the yield moment capacity of the pile and subsequent plastic hinges were formed. Moreover, when the thickness of the liquefied soil was more than half of the entire soil depth, the mobilised bending moments in the piles exceed the ultimate moment capacity of the pile and thus total failure of the piles were observed. In addition, in the absence of liquefied soil layer, the inertial interaction had a dominant impact on the pile response in this study. However, with increasing the thickness of the liquefied layer, further loads were developed in the piles due to amplified kinematic interaction, while the inertial interaction-induced loads decreased.

Concrete liquid storage tanks are commonly used in regions that may be highly seismic, for the storage of water, petroleum products and other chemicals. In some cases, such as for liquefied natural gas (LNG) tanks, a secondary concrete containment is designed for external protection, ignoring any direct contact or interaction with the inner storage liquid by creating a gap, as another inner tank is used to hold the liquid. Typical secondary containment tanks for LNG are circular, upright concrete tanks, with fixed roofs, while the support wall conditions at its base can be hinged or fixed. In this study, the nonlinear behavior of ground supported circular reinforced concrete containment tank under the effect of the seismic loads is investigated for both hinged and fixed wall support conditions. A threedimensional finite element model considering material nonlinearities was included. In particular, the Concrete Damage Plasticity (CDP) model, capturing the possible tensile cracking and compressive crushing of the concrete containment systems under seismic loads was adopted. By adopting time history analyses, deformation and stresses developed in the tank were assessed when subjected to large earthquakes, namely the 1994 Northridge and 1995 Kobe earthquakes, while frequency domain analyses were also conducted, to obtain the natural period and mode shapes for different wall support conditions. The results showed that in the hinged tank, the walls experience higher structural responses (in terms of shear force and bending moment); compared with the fixed tank, particularly around the mid-height zone of the tank wall. Conversely, at the base of the fixed tank, shear forces and bending moments were higher, compared with the hinged tank's base. Under the effects of large earthquakes, both tanks experienced damage, yet larger seismic forces upon a hinged tank could potentially create more damage.

No abstract

The elevated water tanks are high importance structures for the humanity lifelines. These elevated tanks are considered as very sensitive structures for seismic movement conditions. Among the reasons for the damage and failure of elevated tanks is the design of its support systems. For this reason, several theoretical and experimental researchers studied the performance of this type of structure under seismic loading. The present study aims to demonstrate the supporting system effect on dynamic buckling of the elevated water tank, using three dimensional finite element technique the seismic response of two elevated water tanks was established taking into account the following factors; the fluidstructure Interaction (FSI), the wall flexibility, different nonlinear time histories analysis, and the material and geometric nonlinearity. Indeed, the application of three different instability criteria for the critical PGA estimate using two seismic excitations, namely El Centro and San Fernando earthquake. The numerical values are compared and no significant effect is found of the supporting system for convective fundamental frequency; however, strongly disturbed impulsive fundamental frequency. In addition, the effect of supporting system and the frequency content of the earthquake on PGAcr are clearly shown. A percent increase of PGAcr can reach up to 37.48%.